Provide user-override for fetch method

[jeff-zucker]

In rdflib, when a fetcher is defined, there is the possibility for users to define their own fetch method. This can happen with an option when creating the fetcher e.g. fetcher = $rdf.fetcher( store , { fetch : fetch_method }) OR it can be overridden by the user/app by setting a global or window variable in the app to define a different fetch method. This is key for using rdflib outside a browser because we need to define a file-based fetch method but is also needed for example if someone writes a fetch method for Dropbox or other storage.

Currently the global variable to override fetch is named window.solidFetcher. This is wrong - fetcher is the object, fetch is the method and this variable overrides the method, not the object. So that needs changing in rdflib to look for window.solidFetch instead of window.solidFetcher. I guess, for legacy we should support both?

And, we need to allow this user override every place we manually define a new fetcher rather than calling rdflib's method of creating a fetcher. This happens in solid-logic where a fetcher is created using either a hard-coded solid-authn-js fetch method or the window.fetch method. It needs to be modified to accept a user-defined window.solidFetch (OR global.solidFetch in out-of-browser) method. In addition, solid-logic also uses "fetcher" when it means "fetch" so it needs to be changed there too.

[bourgeoa]

I suppose you meant solidFetcher and solidFetch with a small s

[jeff-zucker]

Yes, I corrected my post, thanks.

[bourgeoa]

can you review linkeddata/rdflib.js#530

[bourgeoa]

This is what I propose for solid-ui/src/logic.ts.
To build it locally not having a latest rdflib update I temporarily added the declare global.

• Is it what you expect ?
• Is there a need to also add crossFetch as default like in rdflib ?
• I kept solidFetcher. Is it needed, that is a new fonctionality ?

root@DESKTOP-PIRJOCS:/mnt/d/github/solid/solidos/workspaces/solid-ui# git diff
diff --git a/src/logic.ts b/src/logic.ts
index 3e189cb8..7178fad9 100644
--- a/src/logic.ts
+++ b/src/logic.ts
@@ -5,11 +5,25 @@ import * as debug from './debug'
 import authSession from './authn/authSession'
 import { SolidLogic } from 'solid-logic'

+declare global {
+  interface Window {
+    solidFetch?: any
+  }
+  var solidFetch: Function
+}
+
 const fetcher = async (url, requestInit) => {
   if (authSession.info.webId) {
     return authSession.fetch(url, requestInit)
   } else {
-    return window.fetch(url, requestInit)
+    // solidFetcher is deprecated
+    const _fetch = (typeof global !== 'undefined' && (global.solidFetch || global.solidFetcher)) ||
+      (typeof window !== 'undefined' && (window.solidFetch || window.solidFetcher)) ||
+      window.fetch
+    if (!_fetch) {
+      throw new Error('No _fetch function available for Fetcher')
+    }
+    return _fetch(url, requestInit)
   }
 }

(END)

[bourgeoa]

I have not seen anything to do in solid-logic.
fetcher is used as fetcher.fetch and there is no creation of any fetch function, like fetch = window.fetch or rdf.fetcher

[jeff-zucker]

No, I do not believe that code belongs in solid-logic. All of the creation of the liveStore and the fetcher should happen in rdflib, not in solid-logic. See linkeddata/rdflib.js#528

[jeff-zucker]

there is no creation of any fetch function, like fetch = window.fetch or rdf.fetcher

Right, and that's the problem - there is no way for a user or app to declare a different fetch method.

[bourgeoa]

This is what I propose for solid-ui/src/logic.ts.

Have you look at this 4th comment above

Right, and that's the problem - there is no way for a user or app to declare a different fetch method.

Not sure to understand the argument.
Why can't you call new SolidLogic({ fetch: _fetch }, authSession) from solid-logic. With _fetch being any fetch method you want. This is creating the liveStore.

If there are reasons to create liveStore without SolidLogic then it is a different issue.

[jeff-zucker]

Not sure to understand the argument.

Supporting redefinition of fetch in the solid-logic constructor is not adequate. Apps which make use of SolidOS as a whole need a way to redefine fetch from outside of SolidOS. For example, where would an app using solid-file-client call that constructor? But this is a moot point since Tim has said that this whole part of solid-logic should be moved back into rdflib.

[TallTed]

Have you look at this 4th comment above

@bourgeoa -- I don't know about anyone else, but I am not at all clear which comment you meant by the above string. Please note that the timestamp displayed on each comment is an <a> element with a direct and specific href which you can copy and paste to provide a specific link to the comment you're referencing -- as I'm doing here, to your comment containing the above string.

[bourgeoa]

@TallTed You are right I should not have done that with the github phone app where this function is apparently missing.

[bourgeoa]

@jeff-zucker link to my proposal for solid-ui #72 (comment)